1. Field of the Invention
The present invention generally relates to a speech recognition circuit which uses parallel processors for processing the input speech data in parallel.
2. Description of the Related Art
Conventional large vocabulary speech recognition can be divided into two processes: front end processing to generate processed speech parameters such as feature vectors, followed by a search process which attempts to find the most likely set of words spoken from a given vocabulary (lexicon).
The front end processing generally represents no problem for current processing systems. However, for large vocabulary, speaker independent speech recognition, it is the search process that presents the biggest challenge. An article by Deshmukh et al entitled “Hierarchical Search for Large-Vocabulary Conversational Speech Recognition” (IEEE Signal Processing Magazine, September 1999, pages 84 to 107), the content of which is hereby incorporated by reference, discusses the general concepts of large vocabulary speech recognition. As discussed in this paper, one algorithm for performing the search is the Viterbi algorithm. The Viterbi algorithm is a parallel or breadth first search through a transition network of states of Hidden Markov Models. An acoustic model for words in a lexicon are represented as states of Hidden Markov Models. These states represent phones or n phones in a phone model of the words. The search requires the evaluation of possible word matches. It is known that such a search is computationally intensive.
In order to speed up the processing performed during such a search in a speech recognition system, parallel processing has been explored. In an article by M K Ravishankar entitled “Parallel Implementation of Fast Beam Search for Speaker-Independent Continuous Speech Recognition” (Indian Institute of Science, Bangalor, India, Jul. 16, 1993) a multi-threaded implementation of a fast beam search algorithm is disclosed. The multi-threading implementation requires a significant amount of communication and synchronization among threads. In an MSC project report by R Dujari entitled “Parallel Viterbi Search Algorithm for Speech Recognition” (MIT, February 1992) the parallel processing of input speech parameters is disclosed in which a lexical network is split statically among processors.
It is an object of the present invention to provide an improved circuit which can perform parallel processing of speech parameters.